Both pod and capsule portafilters used in espresso machines have a cylindrical chamber to hold the ground materials, such as coffee, used in brewing. The cylindrical envelope of this chamber is closed and the top and the base of the cylinder are perforated to allow pressurized water to enter the cylinder from one side flushing axially through the ground coffee and exiting as an espresso beverage from the other, perforated side.
Since the espresso preparation procedure involves the use of high pressure water flushing through the brewing materials, such as ground coffee, and this pressure develops very high axial and radial forces on the internal face of the capsule, a very rigid construction is needed to support the capsule during the preparation process. Such rigid construction increases the cost of producing the brewing machine and the cost to the consumer is like-wise higher.